1:1 NAT, also called One-to-One NAT or in some cases “Network Address
Translation”, maps all ports of an external address for a given protocol to an
an internal address. This mapping works for inbound and outbound packets.
To create a 1:1 mapping, make a static NAT entry which does not specify any
ports:

In the above example, a TCP connection to port 222 on 203.0.113.2 will be
forwarded to port 22 on 10.2.0.5. When the packet leaves TNSR, the source is
translated so the connection appears to originate from 10.2.0.2 using a random
source port.

Warning

This feature requires endpoint-dependent NAT mode. In TNSR 18.11
and later, this is the default mode.